A rotary member such as a driving shaft and a gear for transmitting a torque generated in a power source to an intended spot or member unavoidably vibrates due to fluctuation of the input torque itself, fluctuation of a load or friction. A frequency of the vibration changes in accordance with a rotation speed and since higher-mode vibration of secondary vibration or more is generated at the same time, amplitude becomes larger by resonance and hence, noise or deterioration of durability can be caused. Thus, a device or a mechanism for preventing vibration as described above is widely employed in various types of equipment for transmitting power by rotation. Particularly, a fluid coupling provided with a device for damping such torsional vibration inside a cover member is known. Examples thereof are described in Japanese Patent Laid-Open No. 2012-77823, Japanese Patent Laid-Open No. 2011-504986, and Japanese Patent Laid-Open No. 2012-533037.
For example, Japanese Patent Laid-Open No. 2012-77823 describes provision of a dynamic damper and a centrifugal pendulum damper inside the cover member of the fluid coupling with a pump shell and a turbine runner arranged facing each other and arrangement of the dynamic damper being adjacent to the turbine runner. Moreover, in the fluid coupling, a lockup piston is arranged so as to be frictionally engaged with an inner surface of a front cover, and the centrifugal pendulum damper is arranged between the lockup piston and the dynamic damper.
Moreover, Japanese Patent Laid-Open No. 2011-504986 describes a power transmission device in which a rotation speed adaptive type vibration absorber formed by a centrifugal force pendulum device is arranged so as to be adjacent to a turbine wheel in an axial direction. In the power transmission device, a damper device having an elastic member is arranged between a lockup clutch frictionally engaged with a front cover in the axial direction and a rotation speed adaptive type vibration absorber. Moreover, Japanese Patent Laid-Open No. 2012-533037 describes a torque transmission device in which a vibration absorber formed by a centrifugal pendulum and a torsional vibration damper are arranged so as to overlap in a radial direction. In the torque transmission device, the vibration absorber and the torsional vibration damper are arranged between a turbine runner and a converter lockup clutch in the axial direction.
As described in each of the aforementioned Patent Literatures, in the fluid coupling provided with a device for damping torsional vibration inside the cover member, a space for arranging the fluid coupling in a vehicle is restricted, and hence effective use of an internal space of the cover member of the fluid coupling is in demand. That is, inside the cover member, the space for arranging the device for damping the torsional vibration is restricted.
According to Japanese Patent Laid-Open No. 2011-504986 and Japanese Patent Laid-Open No. 2012-533037, a space between the turbine runner and the cover member in the radial direction is not effectively utilized. On the other hand, in the structure described in Japanese Patent Laid-Open No. 2012-77823, a part of the dynamic damper is arranged in a space between the turbine runner and the cover member.
However, in the structure described in Japanese Patent Laid-Open No. 2012-77823, an engagement portion connecting the dynamic damper and the lockup piston covers an outer peripheral side of the centrifugal pendulum damper, and therefore an outer diameter of the centrifugal pendulum damper is restricted by the engagement portion. Therefore, distances from rotational centers of a pump impeller and the turbine runner to a mass body which is the pendulum member become short, and it is likely that an inertial moment by the centrifugal pendulum damper runs short.